Some filter devices contain two or more layers of membrane sandwiched together in order to gain certain performance characteristics such as retention. It is important that each layer remain integral and defect free throughout the assembly process and during its use.
Normally integrity testing is done to the finished product containing the multiple layers through an air diffusion test. This test wets out the membrane layers with a suitable liquid, such as water, alcohol or mixtures of the two (depending on whether the filter is hydrophilic or hydrophobic). Air at a set pressure(s) is applied to one side of the wetted membrane and air flow on the other side is measured. If the flow increase downstream is too quick or at a low pressure, this indicates that there is a defect in the filter or its sealing into the device. The problem with using this test in devices with multiple layers of membrane is that only the overall device is tested and the test can only indicate if there is a defect in all the layers. A defect in one layer may not provide one with a conclusive indication of a defect.
What is needed is a device that allows one to independently test each layer of membrane in an integrated multilayered device. The present invention allows one the ability to do so.